1. Field of the Invention
The present invention relates to a reflector which is resistant to mechanical attack and with high total reflectance, comprising a reflector body and arranged thereon:
a) a functional coating; and
b) a sequence of reflective layers containing one reflective layer and several transparent layers.
The invention also relates to the use of such reflectors.
2. Background
Manufacture of strips of bright materials, e.g. highest grade aluminum or aluminum based AlMg alloys with purity percentage of 99.8% and higher, e.g., 99.9%, and rolled surfaces that produce diffuse or directed light reflection, depending on the application, are generally well-known. For the purpose of increasing directed reflection (degree of brilliance), chemical or electrolytic burnishing followed by anodic oxidation of the surface of strips of this kind, in order to produce a protective layer, e.g. 1.5 xcexcm thick, is also well-known.
The known methods have the further disadvantage that expensive, high grade aluminum based bright alloys with a high degree of purity have to be used. The degree of surface reflectance is reduced by the anodic oxide layer and consequently so are total reflectance and directed reflectance due to absorption and diffuse light scatter, especially in the oxide layer. This results in loss of energy.
EP-A 0 495 755 discloses objects with aluminum surfaces which are suitable for deposition of layer systems on these surfaces from the vapour phase. Anodizing of the surfaces is not carried out and a layer system is described consisting, for example, of an adhesive layer such as a ceramic layer, a light reflecting layer, a metal layer, e.g. aluminum, and one or more transparent protective layers of e.g. oxides, nitrides or fluorides of magnesium, titanium or praseodymium. Such layer systems exhibit a high degree of reflection. A system of this type nevertheless has the disadvantage that the surface is very sensitive to mechanical influence.
EP-A 0 568 943 describes deposition of a reflective layer on an aluminum base layer and a superimposed gel film which has been deposited on the aluminum by a sol-gel process. Reflection is obtained by a layer system comprising silicon dioxide, metal, silicon dioxide and titanium dioxide layers. This is also a possible way of obtaining reflective aluminum materials. The layer structure described in EP-A 0 568 943 is not resistant to mechanical stress to the desired extent.
The purpose of the present invention is to avoid the disadvantages described and to propose reflectors in which the reflecting layer is insensitive to external mechanical influences and which is characterized by high stability against wiping.
According to the invention this is achieved by the sequence of reflective layers containing as the protective layer a silicon dioxide having the general formula SiOx, where x is a number from 1.1 to 2.0, or an aluminum oxide having the formula Al2O3, in a thickness of 3 nm (nanometers) or more, with the protective layer as the surface layer protecting the subjacent layers against mechanical damage and the protective layer shows no surface damage in the wiping test according to DIN 58196 after 50 test cycles of 100 wipe strokes each.